Controlled chemical heating of a well using aqueous gas-in-liquid foams

ABSTRACT

Aqueous gas-in-liquid well circulation foams are useful as agents in the chemical heating of a well, e.g., (1) as a cover or blanketing means for hypergolic reactions carried out in a well, or (2) as a carrier means for the controlled introduction and contacting of one or more reactive chemicals of a high energy reaction system into a well.

United States Patent John C. McKinnell Taft, Calif.

July 17, 1969 Feb. 9, 1971 Chevron Research Company San Francisco, Calif.

a corporation of Delaware lnventor Appl. No. Filed Patented Assignee CONTROLLED CHEMICAL HEATING OF A WELL USING AQUEOUS GAS-IN-LIQUID FOAMS [56] References Cited UNITED STATES PATENTS 2,953,205 9/1960 Carr 166/260X 3,185,634 5/1965 Craig, Jr. et al.. 166/273 3,266,572 8/1966 Woodward 166/260 3,299,953 1/1967 Bernard l66/305X 3,314,477 -4/1967 Boevers et al. 166/260 3,336,982 8/1967 Woodward et al... 166/299 3,410,344 1 H1968 Cornelius 166/309X Primary Examiner-Stephen J. Novosad Attorneys-A. 1... Snow, F. E, Johnston, John Stoner, Jr. and

D. L. Hagmann ABSTRACT: Aqueous gas-in-liquid well circulation foams are useful as agents in the chemical heating of a well, e.g., (1 as a cover or blanketing means for hypergolic reactions carried out in a well, or (2) as a carrier means for the controlled introduction and contacting of one or more reactive chemicals of a high energy reaction system into a well.

BACKGROUND OF THE INVENTION 1. Field of the Invention t This invention relates to the use of aqueous gas-in-liquid foams as agents in the controlled heating of a well, particularly in the heating of an oil well by chemical means.

2. Description of the Prior Art It is known in the art to heat a well by introducing a hot gas, such as steam, into the well and circulating the steam, for example down a pipe string and up the annulus of the well. lt is also known to mix hypergolic fuels in a well in order to effect a rapid heating of a local area in the well. Certain disadvantages are experienced in the foregoing. When steam is circulated in a well, the heating of the well is generalized rather than localized. It is usually relatively inefficient to heat the total well where only localized heating is desired. Often a local intense heating can be effective and satisfactory where a similar heating of the whole well would be technically undesirable. Hypergolic reactions are by their nature difficult to control and if poorly controlled can cause severe blow outs, fires and the like in a well. Hypergolic reaction systems are known in the art; see for example U.S. Pat. Nos. 2,763,619; 2,940,250; and 3,099,132.

SUMMARY OF THE INVENTION lt has now been found that preformed aqueous gas-in-liquid well circulation foams are useful agents for controlling exothermic chemical reactions in a well. Two component hypergolic reactants, fuel and oxidizer, are advantageously mixed under a covering blanket of aqueous gas-in-liquid foam. The foam prevents accumulation of explosive mixtures in the well above the reaction system and serves as an attenuating means where the reaction tends to become excessively energetic. In another aspect, one or both of the liquid components of a two component liquid hypergolic reaction system can be carried into a well in a preformed aqueous gas-in-liquid well circulation foam and mixed at a predetermined location in the well: (l) by mixing two separately introduced preformed foams, and/or (2) by circulating a fuel or oxidant carrying preformed foam into a reservoir of oxidant or fuel in the well. By control of foam flow rate, the rate of chemical heating and degree of heating in the well is correspondingly controlled.

DESCRIPTION OF THE INVENTION In a preferred embodiment of the invention two foamable aqueous solutions are prepared in which eachcontains 0.5- -l.0 percent by weight of the sodium salt of a C, -,-C,,,-nalpha-olefin sulfonate as the active foaming agent. One of the solutions contains about l--35 weight percent of hydrogen peroxide. The other contains l0-35 weight percent of unsymmetrical dimethyl hydrazine and the balance of the solutions is water. Each solution is separately foamed by ordinary means by passing an inert gas and the foamable solution into a foaming unit at a rate sufficient to yield a foam having a volume quotient, standard cubic feet of gas to gallon of foamable solution in the range from about 1 to 50. By means of the annulus, separate pipe strings or a combination thereof the two foams are separately introduced into the well and mixed together by discharge in a common location in the well, for example at the bottom or above a suitably expandable and removable well plug or the like. Upon the intermixing of the two foams the highly exothermic reaction of hydrogen peroxide with the hydrazine derivative results in the effective heating of the well in the zone of the mixing. Alternatively where desirable, one of the reactants may be placed in the well at a desired location in the form of an aqueous solution and the other reactant may be carried into the well and introduced into the solution as a component of a preformed aqueous gasin-liquid well circulation foam.

While fuming nitric acid, red fuming nitric acid and aqueous hydrogen peroxide (5 to 30 percent solutions of the peroxide in particular) are contemplated as oxidizers for use herein, in

view of the relatively higher corrosivity of dilute nitric acid solutions, the use of the foregoing acids is preferably contemplated as liquids into which fuel carrying foams are introduced.

Other representative hypergolic fuels contemplated as fuels herein include lower (C -C organic mercaptols, aldehydes, ketones, organic thiophosphites, disulfrdes, aminosulfrdes, polymethyldiamines and the like organic compounds useful as 'hypergolic fuels as'known in the art (see, for example, the

volume quotient, standard cubic feet per gallon respectively in the range from about 3 to 50.

By a preformed foam, as used herein, is meant a foam which is generated out of contact with the solids and/or liquids naturally encountered-in a well bore, Le, a foam formed out of contact with contaminants associated with a well bore environment, including cuttings, oil, brine, and the like.

The aqueous foams of the present invention are preferably circulated or introduced into a well at velocities less than about 600 feet per minute.

Gas-in-liquid foam generation is well known in the art (see, for example, Encyclopedia of Chemical Technology, Volume 6, Interscience Encyclopedia, Inc., New York (1951); U.S. Pat. No. 3,212,762). Large volumes and a ready supply of foam are required for the practice of the instant invention. An eductor or venturi-type nozzle arrangement followed by downstream inline mixing baffles or steel wool or the like, has

been found to yield satisfactory gas-in-liquid foams and is the preferred mode for use herein.

In the production of the subject foams a gas such as air, nitrogen, methane, natural gas, inert exhaust gas, or carbon dioxide and the like is used. Air is preferred where natural gas pressures are low; at high formation pressures a relatively inert gas, i.e., nitrogen, air and carbon dioxide or carbon dioxide is preferred.

Organic foaming agents are in general satisfactory for use herein provided that at the foaming agent concentration to be used, the aqueous solution has a Ross-Miles initial foam height of at least 10 centimeters and a cumulative foam height of at least 30 centimeters [cf Ross, cf. and Miles, G. D., An Apparatus for Comparison of Foaming Properties of Soaps and Detergents, Oil and Soap, Volume 18, 1941, Pages 99-102; ASTMD 1 173-53 (1965)].

By. a Ross-Miles initial foam height, as used herein, is meant the initial or O-time foam height as obtained in the standard Ross-Miles foam analysis method. l

By a cumulative foam height, as used herein, is meant the sum of the foam heights at the 0-, 1-, 2-, 5- and 10-minute intervals as obtained in the Ross-Miles method.

Useful foaming agent concentrations vary depending upon the particular agent being used. ln general, in parts by weight per 100 parts of foamable solution, the amount of the agent desirably used is in the range from about 0.05 to 2. Larger amounts of foaming agent can also be used, but such use is relatively inefficient in view of the cost, particularly at concentrations in excess of about 3-5 parts per I00. Usually 4 relatively larger amounts of foaming agent are required for tion. These agents are known to the art as surface active compounds and are classified as anionic, cationic, nonionic and amphoteric agents (see, for example, Detergents and Emulsifiers," 1966 Annual. John W. McCutcheon, Inc, also Surface Active Agents, Volumes I and 2, A.M. Schwartz, J.W. Perry and J. Berch. lnterscience Publishers. Inc.. New York (1949 and l958)].

Preferred well circulation foams have, in general, a gas-toliquid volume quotient (standard cubic feet per gallon, respectively) in the range from about 3 to 50, respectively, more preferably in the range from about 5 to 20. For extra heavy duty usage. foams having a quotient as low as I2 may be satisfactory. These foams have a relatively high density and tend to be more difficult to circulate, i.e. have a higher work requirement. On the other hand, with increasing gas-to-liquid quotients, bubble sizes are relatively larger and foam characteristics, including stability under conditions of flow in a well, become progressively poorer.

Anionic foaming agents are preferred for use in the preparation of the subject foamed well circulation fluids. Of these agents, the surfactants of the formula RSO H in which R represents an oleophilic radical, are preferred for use herein. They yield foams which are especially useful well circulation fluids. The oleophilic radical R may be a hydrocarbon radical containing from about 8 to carbon atoms or a radical of the formula R' (OCII CI-I in which R is an oleophilic hydrocarbon radical containing from about 8 to 18 carbon atoms and m is a whole number in the range from I to about 15, preferably 3 to 10, inclusive.

Hydrocarbon radicals in general having the specified carbon atom content are contemplated as groups R or R in the formulas above. Representative classes include such radicals as alkyl, cycloalkyl, aryl, alkylaryl, alkenyl, alkylcycloalkyl, al-

kenylcycloalkyl, alkenylaryl, arylalkenyl, and the like radicals. Preferred hydrocarbon radicals are the aliphatic or alkylaryl hydrocarbon radicals.

Representative preferred classes of foaming agents useful in the instant invention include the water soluble salts of alkylbenzene sulfonic, the paraffin sulfonic, the alpha-olefin sulfonic, the internal olefin sulfonic acids and the like. Of these foaming agents, the class of alpha-olefin sulfonates is particularly preferred. These materials are a complex mixture of compounds which yield foams which are especially effective well circulation fluids. In general, they yield foams which are dense and made up of relatively uniform small bubbles. The small bubble sizing appears to promote foam stability and to impart to them excellent circulation characteristics.

By definition, as used herein, by the term alpha-olefin sulfonate is meant the product mixture obtained at a reaction temperature in the range from about 10 to 60 C. from the reaction of an alpha-olefin, RCI-I=CI-I where R is an alkyl radical of the C C range, with sulfur trioxide diluted by air with the product being neutralized and hydrolyzed at a temperature in the range from about 50 to 130 C. [See, for example, AIpha-Olefins in the Surfactant Industry" by TH. Lid dicoet, The American Oil Chemists Society, Nov., 1963, Volume 40, No. II, pp. 63l-636, and Alpha-Olefin Sulfonates from a Commercial SO -Air Reactor by D.M. Marquis et al., ibid, Volume 43, No. l I, pp. 607-614 (1966).

The use of molecular mixtures ofa given foaming agent species as well as individual molecular species of the aforedescribed organic foaming agents is contemplated. Mixtures which contain two or more foaming agent species are also contemplated. In particular, of the mixtures of foaming agent species, the alkylbenzene sulfonates and alpha-olefin sulfonates are preferred for use in the production of foams in which each foaming agent species is in turn a molecular mixture, for example, a C -C, -aIkylbenzene sulfonate molecular mixture plus a C ,.,-C alpha-olefin sulfonate mixture.

Representative foaming agents useful in the practice of the subject invention include water soluble salts of polypropylene tetramer benzene sulfonic, polypropylene pentamer benzene sulfonic, n-dodecylbenzene sulfonic, stetradecylbenzene sulfonic, s-hexadecylbenzene sulfonic acids, n-c -C -alphaolefin sulfonic acid mixtures, n-C, -,-C ,-internal olefin sulfonic acid mixtures and the like. h

The following examples further illustrate the invention.

EXAMPLE I Aqueous solutions containing hydrazine or hydrogen peroxide and a sulfonate foaming agent yielded excellent stable foams when air was introduced into the solutions.

EXAMPLE 2 A covering of aqueous gas-in-liquid foam was placed over a solution of hydrazine and an aqueous hydrogen peroxide solution was added dropwise through the foam into the hydrazine solution. A vigorous reaction took place upon the contacting of the reactants. The column of foam appeared to modify, attenuate the reaction.

EXAMPLE 3 Five drops of 30 percent hydrogen peroxide were added' into 50 cc. of 30 percent aqueous hydrazine. The initial temperature of the hydrazine solution was 35 C. 15 seconds after the addition the solution temperature had increased to 48 C.

EXAMPLE 4 The hydrazine solution of example 3 was diluted by the addition of 50 cc. of water. About 1 cc. of 30 percent hydrogen 2. The improvement as in claim I further characterized in that said foam is employed as a cover for said reaction.

3. The improvement as in claim 1 further characterized in that said foam is used as a carrier for at least one of said components.

4. The improvement as in claim 1 further characterized in that said well is an oil well.

5. In the heating of a well by means of an exothermic two component chemical reaction, the improvement which comprises separately incorporating said components into separate preformed aqueous gas-in-liquid foams, separately introducing said foams into a well and mixing said foams at a predetermined zone in the well, thereby heating said zone by the resulting exothermic chemical reaction.

6. The improvement as in claim 5 further characterized in that said reactants are hydrazine and hydrogen peroxide.

7. The improvement as in claim 5 further characterized in that said reactants are unsymmetrical dimethyl hydrazine and hydrogen peroxide.

8. In the heating of a well by means of an exothermic two component chemical reaction, the improvement which comprises placing one of said reactants at a predetermined zone in the well, incorporating the second of said reactants into a preformed aqueous gas-in-liquid foam and circulating said foam into contact with said first reactant.

9. The improvement as in claim 8 further characterized in that said first reactant is fuming nitric acid and in that said second reactant which is incorporated in the foam is an organic hypergolic fuel.

10. The improvement as in claim 8 further characterized in that said first reactant is aqueous hydrogen peroxide and in that said second reactant which is incorporated in the foam is selected from the group consisting of hydrazine and unsymmetrical dimethylhydrazine. 

2. The improvement as in claim 1 further characterized in that said foam is employed as a cover for said reaction.
 3. The improvement as in claim 1 further characteRized in that said foam is used as a carrier for at least one of said components.
 4. The improvement as in claim 1 further characterized in that said well is an oil well.
 5. In the heating of a well by means of an exothermic two component chemical reaction, the improvement which comprises separately incorporating said components into separate preformed aqueous gas-in-liquid foams, separately introducing said foams into a well and mixing said foams at a predetermined zone in the well, thereby heating said zone by the resulting exothermic chemical reaction.
 6. The improvement as in claim 5 further characterized in that said reactants are hydrazine and hydrogen peroxide.
 7. The improvement as in claim 5 further characterized in that said reactants are unsymmetrical dimethyl hydrazine and hydrogen peroxide.
 8. In the heating of a well by means of an exothermic two component chemical reaction, the improvement which comprises placing one of said reactants at a predetermined zone in the well, incorporating the second of said reactants into a preformed aqueous gas-in-liquid foam and circulating said foam into contact with said first reactant.
 9. The improvement as in claim 8 further characterized in that said first reactant is fuming nitric acid and in that said second reactant which is incorporated in the foam is an organic hypergolic fuel.
 10. The improvement as in claim 8 further characterized in that said first reactant is aqueous hydrogen peroxide and in that said second reactant which is incorporated in the foam is selected from the group consisting of hydrazine and unsymmetrical dimethylhydrazine. 